Image:Acorns small to large.jpg|thumb|Acorns from small to large of the Willow Oak, ''Quercus phellos'' (very small, at center); the Southern Red Oak, ''Quercus falcata''; the White Oak, ''Quercus alba''; and the Scarlet Oak, ''Quercus coccinea''; from southern Greenville County, SC, USA. Scale bar at upper right is 1 cm.
File:Acorn diagram.jpg|thumb|Diagram of the anatomy of an acorn: A.) Calybium and cupule|Cupule B.) Pericarp (fruit wall) C.) Seed coat (Testa (botany)|testa) D.) Cotyledons (2) E.) Plumule F.) Radicle G.) Remains of Gynoecium|style. Together D., E., and F. make up the embryo.
The '''acorn''', or '''oak nut''', is the nut (fruit)|nut
of the oak
s and their close relatives (genera ''Quercus
'' and ''Lithocarpus
'', in the family Fagaceae
). It usually contains a single seed
(occasionally two seeds), enclosed in a tough, leathery shell, and borne in a...